The efficiency of chemical processes is becoming an increasingly important issue with the growing requirements of waste reduction and minimization of emissions of volatile compounds in air and water streams. Analytical on-line analysis of such streams can play a vital role in achieving and maintaining optimum process operating conditions.
As opposed to off-line analysis, on-line analysis can provide more efficient use of information about a process in terms of the amount of data, the quality of data, and the ability to respond to changes in the process as indicated by the data. For example, obtaining continuous temperature measurements by means of a thermocouple can provide a more statistically useful data set and more precise indications of changes in the process temperature than ca be obtained from intermittent manual measurements using a thermometer. The same is true for other traditionally measured process parameters such as pressure and pH, as well as the more sophisticated measurements of the composition of a chemical process.
Currently, on-line process composition analyses often are obtained from chromatographic, spectroscopic, or solid state chemical sensor techniques, as dictated by the nature of the analyte(s) and the process matrix. Although the speed, sensitivity, and selectivity of mass spectrometry make the technique attractive, on-line analysis by mass spectrometry has until recently been limited to clean, well-defined gas phase streams.
Sampling generally is the most difficult problem associated with the on-line analysis of process streams, regardless of the analytical technique. Many gas and liquid process streams are chemically and physically complex and require pretreatment prior to analysis. This has been especially true for mass spectrometry analysis, which generally has utilized a capillary or orifice sample introduction system that is limited to filtered fluids.
Many sampling problems are circumvented by utilizing membrane extraction techniques. In practice, the analysis of organic compounds of interest in liquid and gas streams is most commonly performed off-line after first extracting and concentrating the compounds. In many instances streams containing particulate matter must be filtered prior to analysis. These procedures often are laborious, time-consuming, and require a considerable amount of sample handling. By use of the apparatus and methods according to the invention, however, the on-line extraction and analysis of samples of process liquid and gas streams may be performed continuously, virtually simultaneously, and without the necessity of filtration.
Prior activities in the relevant art have focused on the measurement of compounds contained in the effluent of gas or liquid streams following the treatment thereof in a reactor. The concept of near-simultaneous on-line analysis of both the influent and effluent gas and liquid streams of a reactor, or a plurality of reactors, has not previously been reported. Nevertheless, for complete and accurate characterization of a process, all streams, both influent and effluent, must be analyzed if errors made from assumptions about the content of the influent stream or streams are to be avoided or minimized. The apparatus and method of the invention achieve this objective.